The influence of mechanical stresses on the characteristics of laser-ultrasonic signals in the vicinity of a hole in silicon nitride ceramics

The experimental study of behavior of laser-ultrasonic signals in the vicinity of a hole in dielectric silicon nitride ceramics under the action of mechanical stresses has been implemented. The key discrepancy between the obtained results and similar results that we obtained earlier for metals was found, along with their quantitative mismatch with the predictions of the thermodynamic model for generation of thermoelastic signals in prestressed materials. An explanation of the observed discrepancies has been proposed based on a model of thermal excitation of defect states in a lattice that we have previously proposed.